1. Field of the Invention
This invention relates generally to development apparatus for mixing and applying developer material to a latent image on an image-bearing member in an electrostatographic reproduction machine, such as a copier or printer. More particularly, this invention relates to such a development apparatus that includes a dual-flow developer material mixing ribbon blender which has an interstream mixing member.
2. Description Relative to the Prior Art
Development apparatus, for example a magnetic brush development apparatus are well known for mixing and applying developer material to a latent image in an electrostatographic reproduction machine such as a copier or printer. Such a development apparatus typically includes an elongate housing which has a sump portion for containing the developer material. Where the developer material comprises a mixture of carrier particles and toner particles, these particles are usually moved and mixed by a mixing device in the sump portion of the housing for triboelectrically charging the particles, as well as for achieving uniformity for example (a) in the concentration of toner particles throughout the sump portion, and (b) in the distribution of developer material within the sump. The mixed and charged developer material can then be fed from the sump portion for application to, or development of the latent image.
The quality of such an application or image development depends, in significant part, on factors such as the level of charge on the toner particles achieved triboelectrically for example, and such as the level and uniformity of the concentration of toner particles in the developer material being applied. As is well known, these factors are mainly determined by the effectiveness of a mixing device used in the sump portion of the development apparatus housing for moving, mixing and charging the developer material particles.
Various such mixing devices are disclosed, for example, in U.S. Pat. Nos. 5,016,053 issued May 14, 1991 to Ibuchi et al; 4,996,565 issued Feb. 26, 1991 to Herley; 4,980,724 issued Dec. 25, 1990 to Tanaka; 4,974,023 issued Nov. 27, 1990 to Aimoto et al; and 4,956,675 issued Sep. 11, 1990 to Joseph. The single mixing device disclosed in the Joseph Pat. No. 4,956,675 is a dual-direction flow ribbon blender and thus can be advantageously used in a single sump development apparatus.
Conventional dual-flow ribbon blenders as disclosed for example in the Joseph Pat. No. 4,956,675 unfortunately tend to create problems such as non-uniform distribution of freshly added toner particles to developer material in the sump of the host development apparatus, and long term uneven distribution or accumulation of developer material within such a sump. The net result is uneven toner concentration and even poor image development. These problems are believed to be associated (a) with difficulties in balancing for example the inner flow rate of developer material in one direction with the outer flow rate of the same in an opposite direction, and (b) with the inner flow stream of developer material being essentially parallel to the outer flow stream thereof.